The present invention relates to a downhill ski.
As shown schematically in FIG. 1, every ski is known to present a camber, i.e. a downwardly concave curved longitudinal profile, so that when it rests in an unstressed state on a surface, it is raised in its central region 1 (between the heel fixing unit T and the front jaw P of the binding), compared with the tail 2 and shovel portion 3, i.e. the section 4 where the tip curvature commences.
This camber ensures stability during straight-line skiing, however when associated with a certain flexural rigidity it can penalize maneuverability along curves. In this respect, when the skier travels through curved trajectories, assuming that inclined position to achieve a state of instantaneous dynamic equilibrium induced by centrifugal force, the ski no longer adheres to the ground flatly, but instead along its laminated edges and has to counter-flex to assume an elastic deformation with downward convexity (FIGS. 2, 3).
The shape of this elastic deformation, assumed by most commercially available skis, resemble a circular arc (line C of FIG. 2). Experimental trials have shown that during initial access to the curve and then during travel along it, the ski obtains a decided advantage in terms of adherence to the ground, lateral holding, stability and slidability by a shape which, along the front portion of the ski, resembles an elliptical arc much more than a circular arc (line E of FIG. 2), i.e. the elastic counter-flexural deformation concerns the front portion of the ski much more than the central portion 1, to an extent which increases towards the shovel portion 3.
This theory emerges more rationally on examining the distribution of the ground reaction load on the laminated edge of the ski when in an angled position. This distribution (confronting the gravitational and centrifugal action F of the skier) must adequately involve the entire length of the ski, including its ends, particularly the front end, in a sufficiently regular form and to a significant extent (full line in the example of FIG. 4), rather than disproportionately to an insignificant extent (dashed line of FIG. 4), as happens in the majority of commercial products (even those intended for sporting and/or competitive use).
There is in fact an increasing tendency to give the ski a considerable softness, with a consequent unfortunate concentration of the reaction load at the centre (dashed line of FIG. 4). The ability to load the ends is therefore based on a very wide sidecut configuration at the tail and in particular at the shovel portion, in accordance with known carving skis. However this expedient, combined with the said basic softness, results in a load distribution in no way equitable and progressive, but in fact incongruously disproportionate, i.e. an excessive absolute maximum at the centre, excessive relative end maximums, and intermediate regions of almost zero load (dashed line of FIG. 4).
In effect, if only the geometry (sidecut) is varied, a sufficiently effective reaction load distribution can be achieved by giving the ski a considerable rigidity (hence penalizing maneuverability, adherence to the ground and slidability). In contrast, in the case of adequately flexible skis, a partial improvement can be achieved by using an interface plate between the ski and boot, to transmit the skier's action to it in a less concentrated manner. As shown schematically in FIG. 5, a plate fixed to the ski close to its ends can divide the load F exerted by the skier into two forces, F′ and F″, so beneficially influencing the reaction load distribution. A substantially similar effect could be achieved by a plate fixed to the ski by supports providing more or less large-area or totally continuous contact. In all cases the benefit can only mainly (or exclusively) concern the central region of the ski, and only marginally involve (or not involve) the shovel portion.
If a more involved design in terms of elasticity is to be attempted, the ski must be made rigid along a considerable length of the central region and of that portion behind the front jaw, to then suddenly become flexible by abruptly tapering its thickness in proximity to the shovel portion.
However this can penalize the equipment in terms of fragility and twistability. Hence a structure must be used which is suitable only for the highest level (exclusively reserved for high-level competition), with excessively sophisticated design and production procedures, in contrast to modern requirements of industrial efficiency and economy.
It is an object of the invention is to overcome these contradictions by providing a ski having adequate flexibility with good reaction load distribution.